An implementation for in-cell optical touch frequently used by conventional arts employs a photo sensor disposed in a pixel to realize external touch by sensing light shielding or reflection caused by a finger.
Specifically, according to the conventional art, in a photo sensing circuit in each pixel element on a touch panel, a transistor (which will be referred to as a “read-out transistor” hereafter) having a gate electrode connected to a scan line is disposed. In the meantime, one of a source electrode and a drain electrode of the transistor is connected to a data line and the other is connected to a capacitor for storing a touch signal. As a result, the transistor may scan and read out the touch signal of each pixel element.
However, as there may be current leakage with the read-out transistor, when a touch signal of a certain row of pixel elements is scanned and read out, the data line may receive noise signals generated by current leakage of other rows, which will cause misreading. On the other hand, to improve the response speed of touching, the read-out transistor has to finish reading the touch signal within a short time, which requires a large enough size of the read-out transistor. However, such a requirement will significantly reduce the aperture ratio of the pixels.